Article 590 discusses temporary wiring.
Temporary wiring is exempt from many of the requirements for "regular" wiring. One need not use junction boxes for splices; we have an enormous amount of lattitude as to support, strain relief, and the like.
There are only two issues that I see. The panel cover is one; concievably, all these wires could simply pass through an unrpotected hole in the panel- or even between the cover and the case.
The other issue is the lack of GFI protection of these "temporary" circuits.
